Power tools such as circular saws, saber saws and routers are used for cutting, ripping, plowing rabbets and dados and shaping wood and other materials. Each of these tools require the operator to have firm control of the tool and unobstructed view of the cut-line in order to produce a straight and accurate cut along a prescribed cut-line during operation. All of these tools produce significant amounts of sawdust that obscures the cut-line. In addition, any variation in the amount of force applied to the tool as well as normal wear factors such as dulling of saw teeth or cutter edges and varying alignment in the teeth of the saw blades, causes the cutter or blade to drift resulting in binding, kickbacks and errant cuts. In addition, the operator is prone to human error caused by fatigue or distraction resulting in a tool deviating from its cut-line causing binding and kickback or simply an errant cut producing unwanted waste.
A variety of fixtures and saw guides have been proposed to address the before mentioned problems but they have deficiencies and limitations including:
A. Complex and intricate designs that involve many parts, are cumbersome to use, expensive to manufacture and generally not practical for the average woodworker,
B. Attachment mechanisms that do not restrain the tool base securely and are susceptible to vibrating loose creating a potential for binding, kickback and danger to the operator.
C. Attachment mechanisms that do not lock the tool base in alignment with the cut-line requiring constant attention to the alignment setting of the tool in the saw guide,
D. Clamping mechanisms designed to secure the guide rail to the workpiece that are complex and limited in their application,
E. Movement of the tool guide along the guide path is subject to binding and restriction due to collection of sawdust and debris,
F. The tool guide does not adequately restrict lateral or radial movement of the tool on the workpiece,
G. The support by the tool guide does not prevent the tool from tilting while in use, which gives rise to binding or kick-back,
H. The length of the guide rail unduly limits the length of cut.
U.S. Pat. No. 4,059,038 uses a complex frame of multi-layer construction that sandwiches a guide piece consisting of a consumable piece of compressed board that forms the reference edge. The guide rail incorporates a trough that a guide plate slides in and the guide plate attaches to tool base with hand-tightened bolts or wing nuts in slots cut in the guide plate. The trough is uncovered and is a collection point for sawdust that can result in binding and restricted movement of the guide plate longitudinally through the trough. The wing-nut attachment mechanism does not ensure a secure fit or precise alignment of the tool to the cut-line. The margin between the slot and the bolt/wing-nut that fastens the saw to the guide plate has freedom of movement that can result in the saw being misaligned to the cut-line. The saw base overhangs the guide plate enabling the saw to tilt during operation resulting in binding and kick back. This can occur as the trough fills with sawdust and the saw guide begins to ride atop of the sawdust tilting the saw. The alternative L-shaped guide rail provides a rigid straight edge along which the base of the saw is manually held during cutting, however, it does not restrict lateral movement of the saw drifting away from the rail that is caused by variation in saw tooth set or dullness of the saw blade or lateral forces applied by the operator.
U.S. Pat. No. 4,335,512 uses complex design involving a pair of elongated ball bearing telescoping slides, a plate to attach the circular saw to the slide assembly, a spring loaded take-up spool that limits the length of travel and a protractor fence. The travel length of the saw is limited to approximately twice the length of the slide rails, which for practical reasons is more appropriate for shorter cuts. The elaborate rail within a rail configuration forms a raceway that contains a ball bearing assembly. The raceway when fully extended to begin a cut exposes the lower portion of the rail assembly that is U-shaped and is a collection point for sawdust. The ball bearing guide assembly that attaches the upper half of the rail to the lower half of the rail operates on a close tolerance and will be severely impacted by the collection of sawdust within the rail assembly. Also, when the spring loaded tape is taken up by the spool, it will entrain sawdust that will cause binding of that mechanism. The attachment mechanism, while designed to keep the base of the circular saw close to the workpiece to maximize the saw's depth of cut, has elongated slots and bolt/wing-nuts to fasten the saw base to the guide rail and has freedom of movement. The normal use and vibrations caused by the operation of the saw can cause the saw to become misaligned resulting in binding and possible kick-back.
U.S. Pat. No. 4,522,098 incorporates a complex and intricate design that includes an integrated adjustable cam locking mechanism, a surface for the saw to ride upon and a raised edge, which the saw is held against during operation.
U.S. Pat. No. 5,964,041 shows a guide tool similar to that of U.S. Pat. No. 4,522,098 with similar disadvantages and deficiencies.
U.S. Pat. No. 6,101,729 incorporates an elaborate frame and an unconventional mechanism to lock the frame onto a workpiece, using non-slip surfaces, adjustment blocks and cap-screws. The frame has a raised edge that the saw base is held against during operation. The saw base is not captured by the saw guide, thus; it does not restrict lateral movement of the saw away from the rail creating a potential for binding or kick-back as well as the potential for the saw base to tilt as it moves away from the raised edge and off of the frame supporting the saw. The width of the frame is such that the initial cut with the saw cuts off the excess portion of the frame that then establishes the reference edge for future cuts. This approach at establishing a reference edge has limitations, however. If a beveled cut is made with the saw, the reference edge is altered rendering it useless for further cuts with the saw blade aligned vertically.
U.S. Pat. No. 5,815,931 discloses an L shaped frame that partially captures the saw base which supports a pair of perpendicular guide arms. The primary guide arm extends laterally from the guide plate and is used to guide the saw along the cut-line by tracking against the edge of the workpiece. The second guide arm is perpendicular to the first and extends longitudinally from the guide plate and serves to limit the length of travel and therefore the length of the cut. The guide plate partially captures the saw base enabling the saw to tilt while operating causing binding and kickback. The guide plate is attached to the saw base with tensioning screws that can vibrate loose. The guide plate does not capture a guide rail or a separate straight edge but relies on the workpiece having a straight edge that forms the reference edge, consequently cannot be used on a workpiece that does not have a finished or joined edge or for making angle cuts that are not parallel to the reference edge. The guide arms do not restrict lateral movement of the saw in the direction of the reference edge of the workpiece enabling the saw to deviate off the cut-line. The width of the cut is limited by the practical length of the guide arms. In order to rip down the center of a sheet of plywood, the guide arm would have to be in excess of 24″ long, allowing for the end of the guide arm that is captured by guide plate. This would result in the drag forces acting between the reference edge of the workpiece and the guide arm to create a radial force with the end of the guide rail contacting the reference edge of the workpiece acting as the pivot point. This would cause the tool to turned into the workpiece causing binding and kickback. Collection of saw dust in front of the guide plate and guide arms will restrict the movement of the saw guide and will further exacerbate the drag and pivotal reaction of the guide arm against the reference edge causing a rotational force that can result in binding and kickbacks.
U.S. Pat. No. 6,079,309 discloses a guide rail with an integral clamping assembly, and with the saw base attached to the guide rail using a single point attachment bar that rides atop of the guide rail. The guide rail and attachment bar that rides atop of the guide rail are susceptible to sawdust collecting on the rail and impacting the freedom of movement along the longitudinal path. The attachment bar captures the guide rail and attaches to the front of the saw under tension from one screw. The tool base is not fully captured by the attachment mechanism and with the single point contact it is susceptible to vibrating loose. With the attachment bar secured only in the forward position of the saw base, the saw can rotate away from the guide rail upon application of a lateral force. During operation, the major component of force is applied to the tool in the longitudinal direction along the cut-line; however, with an operator positioned along side of the tool during operation, a nominal lateral force is to be expected.
The guide tool of U.S. Pat. No. 6,101,729 uses an L shaped guide forming a perpendicular set of rails that facilitate the cross cutting of lumber. Such a tool guide has very limited applications, facilitating cross cutting operations only. The guide is essentially a pair of perpendicular rails or straight edges along which the base of the saw is manually held during cross cutting and it does not restrict lateral movement of the saw away from the rail that can result in binding or kickback.
U.S. Pat. No. 6,173,631 use a frame having raised edge that the saw base is held against during operation. Saw base is not captured by the saw guide, thus; does not restrict lateral movement of the saw away from the rail creating a potential for binding or kick-back. The width of the frame is such that the initial cut with the saw cuts off the excess portion of the frame that then establishes the reference edge for future cuts. This approach at establishing a reference edge has limitations, however. If a beveled cut is made with the saw, the reference edge is altered rendering it useless for future cuts.
The saw guide of U.S. Pat. No. 6,216,355 uses a calibrated scale that attaches to the front of the saw and a guide pin that tracks upon one straight edge of the workpiece. The guide does not capture a guide rail or a separate straight edge but relies on the workpiece having a straight edge or reference edge and consequently cannot be used on a workpiece that does not have a finished (joined) edge nor can it be used for making angle cuts, that is, cuts not parallel to the reference edge. The guide pin that tracks the straight edge of the workpiece does not restrict lateral movement of the saw in the direction of the reference edge of the workpiece enabling the saw to deviate off the cut-line. The width of the cut is limited by the practical length of the gauge. In order to rip down the center of a sheet of plywood, the gauge would have to be in excess of twenty-four inches long, allowing for the end of the gauge that is attached to the saw plate. This would result in the drag forces acting between the reference edge of the workpiece and the guide pin to create a radial force with the guide pin contacting the reference edge of the workpiece acting as the pivot point. This would cause the tool to be turned into the workpiece causing binding and kickback. Collection of saw dust in front of the gauge restricts the movement of the gauge and further exacerbates the drag and pivotal reaction of the guide pin against the reference edge causing a rotational force that results in binding and kickbacks.